Indoor Pools


New member
Jan 29, 2020
Nashville, Tennessee
Hello Community!

First, I would like to thank you for sharing your knowledge and wisdom. I appreciate having these forums as a resource and have done extensive research and reading while on my quest to conquer a recurring issue I'm having. Thank you in advance for your helpful comments and suggestions!

The Problem:
We have several cabins in the Smoky Mountains with indoor swimming pools. They are small so perhaps "plunge pools" would be more appropriate. Every few months the pools become cloudy and I get a phone call from the management company telling me they can't figure out what is wrong. I make the drive up there and always find the same thing.

The Levels:
  • = 0 ........... Total Chlorine
  • = 0 ........... Free Chlorine
  • > 240 ....... Alkalinity
  • > 8.4 ........ pH
  • > 300 ....... Cyanuric Acid
Things I've Tried
Typically, adding shock and muriatic does nothing. I've tried different types of chlorine and other products that have been recommended to me in the stores which do nothing. I have called "professionals" for help who can't figure it out either, so, I end up throwing in a sump pump and draining the water.

At first, I tried draining a quarter of the pool. When that didn't work, I tried half. After a lot of time and effort, I just started draining and refilling the entire thing. After doing this several times, I decided it would be a good idea to see about automating the pool chemistry maintenance. A local company talked me into adding automatic chlorinators to every pool, which I did. Guess what? It's still a problem!

Here's What [I think] Is Happening

  1. We are adding stabilized chlorine to indoor pools
  2. Indoor pools don't have to worry about the sun burning up the chlorine
  3. Cyanuric acid levels build up causing the pool to lock up [but no one knows this]
  4. We add more and more chemicals which take no effect
  5. Cyanuric acid levels continue to climb
  6. TDS exceeds the point at which water can be chemically treated
  7. We have no choice but to drain and refill
I came across this from Water Safety Magazine:
Myth #1: “Chlorine is Chlorine, it’s all the same.”
There are 5 types of Chlorine; Sodium hypochlorite, Lithium hypochlorite, Calcium hypochlorite, Dichlor, and Trichlor. The first difference is Sodium, Lithium, and Calcium are un-stabilized Chlorine. Dichlor and Trichlor are stabilized. Stabilized chlorines have Cyanuric Acid which acts as a type of sunblock for the Chlorine. The sun will break down Chlorine causing it to burn off quicker; Cyanuric Acid slows this process down. Therefore, Dichlor and Trichlor are used in outdoor pools as pucks/tablets. Because indoor pools do not need to worry about the sun, and do not need Cyanuric Acid, they usually use the other 3.
My Questions
  1. Am I on the right track?
  2. Will switching to NON-STABILIZED chlorine help solve the problem?
  3. If so, where can I find this product for in-line feeders? Most products online don't provide all the details needed to make a decision on what type of chlorine it is.
Thank you again for your help. I can't wait to read what everyone thinks!

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Welcome to TFP! :wave: So basically you are correct. I wouldn't worry about item 6 (TDS). But a major water exchange is the only way to lower the CYA. For indoor pools, you can get-by with a CYA of about 20, no more than 30 I'd say. From there we use the FC/CYA Chart to keep the FC and CYA balanced. As for chlorine, liquid pool chlorine (aka regular bleach) works with no stabilizer in it. I will say this however, check your local rules for public pools. There may be some mandatory guidance in your county for public pools and such.

Stick around and make sure to review our ABCs of Pool Water Chemistry and other links. Lots of great help here.

PS - Your pH (and TA) is too high as well. Muriatic acid will bring that down. But the water exchange should be priority #1. Also, please confirm how you are testing your water. You'll get asked that often. :)


Gold Supporter
TFP Guide
Nov 12, 2017
Central California
Hi, and welcome to TFP! You're in good hands now. Please read this, and follow those instructions as best you can, it'll help you get a better answer. And while you're at it, please specify what you mean by "automatic chlorinators."

Possible bad news: if that company sold you tab feeders, they should take them all out and refund your money! There is no such thing as unstabilized tabs. And you're already on to what the problem is. The solution might have been SWGs for each pool, but we'll get into that more depending on your description of the pools.


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Who maintains the pools with what frequency?

What test kits do they use?

Can someone service the pool every day or two?
Last edited:


Mod Squad
LifeTime Supporter
Jan 17, 2012
Evans, Georgia
there are unstabilized calhypo tabs, but of course they add calcium
And if using CalHypo tabs/sticks they NEVER go into the inline Rainbow style chlorinator that's had regular chlorine pucks in there! That is a recipe for disaster <kaboom!> as the two types of chlorine *do not play well together!!!*.

You have to use a specific Calhypo dispenser/floater


In The Industry
Feb 25, 2020
omaha, ne
Been using Cal Hypo tabs for years now. Accu-Tab is an stabilized puck that does work with it's own type of dispenser. Their inline erosion feeder is not much different than the rainbow style feeder (Gravity or Suction erosion feeders all work the same). I have heard from a guy I know he used them in a NEW rainbow style feeder with no problems, you just have to figure out your own setting. We used the Powerbase 1030 for the last 3 years trouble free.


Mod Squad
Gold Supporter
Platinum Supporter
LifeTime Supporter
Jul 16, 2012
Central MD
Talbot - Given that you are in Nashville, I certainly hope all is well. Probably much bigger concerns in your area than pool maintenance now.

If the pool(s) are still on your mind, do you have any thoughts or follow-up on the advice given? I know we asked a few follow-up questions but saw no feedback.